-LRB- CNN -RRB- -- Police arrested another teen Thursday , the sixth suspect jailed in connection with the gang rape of a 15-year-old girl on a northern California high school campus .

Jose Carlos Montano , 18 , was arrested on charges of felony rape , rape in concert with force , and penetration with a foreign object , said Richmond Police Lt. Mark Gagan .

Montano was arrested Thursday evening in San Pablo , California , a small town about two miles from the city of Richmond , where the crime took place .

Montano , who was held in lieu of $ 1.3 million bail , is accused of taking part in what police said was a 2 1/2 - hour assault on the Richmond High School campus .

Police said as many as 10 people were involved in the rape in a dimly lit back alley at the school , while another 10 people watched without calling 911 .

The victim was taken to the hospital in critical condition , but was released Wednesday .

Four other teenage suspects were arraigned Thursday on charges connected to the rape .

Cody Ray Smith , described by the court as older than 14 , pleaded not guilty to charges of rape with a foreign object and rape by force .

Two other juveniles , Ari Abdallah Morales and Marcelles James Peter , appeared with Smith at the Contra Costa County Superior Court , but did not enter a plea . The court described Morales as younger than 16 , and did not give an age for Peter .

All three juveniles , who wore bulletproof vests at the hearing , were charged as adults .

A fourth person , Manuel Ortega , 19 , appeared separately without an attorney and did not enter a plea . He did not wear a protective vest .

Another person , Salvador Rodriguez , 21 , was arrested Tuesday night , but he was not in court Thursday .

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Another arrest made in gang rape outside California school

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Investigators say up to 20 people took part or stood and watched the assault

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Four suspects appeared in court Thursday ; three wore bulletproof vests